1. Field of the Invention
This invention relates generally to radiation or heat curable coating compositions for a variety of articles, particularly plastic ophthalmic lenses, and more particularly to dual coated ophthalmic lenses with high abrasion and scratch resistance.
2. Description of the Related Art
Plastic materials have found increased usage for the construction of a variety of substrates, including but not limited to ophthalmic lenses for eyeglasses, cameras, and optical instruments, due to their light weight, ease of fabrication and relatively low cost. Common lens forming materials include CR-39 (diethyleneglycol bisallyl carbonate) available from PPG Industries, bisphenol A polycarbonate (PC), and poly(methylmethacrylate) (PMMA).
Plastic lens materials have traditionally possessed inferior resistance to scratching, commonly evaluated by rubbing the surface with steel wool; and inferior resistance to abrasion, usually measured by shaking the lens surface under a bed of sand in the Bayer Abrasion Test. The cumulative effect of scratching and abrading the lens surface is to increase the haze in the lens and ultimately to produce a substantially translucent lens incapable of providing a coherent image. Consequently, plastic lens surfaces have required treatment to provide a scratch and/or abrasion resistant layer on the lens surface to increase the field durability of the lens, and retard the development of haze.
With current lens coating formulations, there is a trade off in the desired properties of scratch resistance and abrasion resistance. One is usually sacrificed for the other.
There is a need for a coating formulation for a plastic substrate that does not sacrifice the scratch resistance or the abrasion resistance for the other. It would be desirable to provide a dual coating for a plastic substrate that provides the substrate with scratch and abrasion resistance characteristics that are substantially similar to glass.